I swear I'm not trying to force people to stop using IE.
However, it's very difficult for me to test it on IE...and even if the pages look fine, the program itself might be handling things differently, caching pages that shouldn't be cached, and who knows what else. Firefox, Opera, and Safari aren't perfect either. They all have their pluses and minuses.
By the way, the server has been up and running without problems for quite some time. It is not showing a high load and is not under stress.
We don't need to upgrade the server hardware just yet. The problems lie somewhere else right now--either with our software (possible yet there haven't been in problems in the time that you mentioned) or with the Internet in general. Lag and "downtime" problems can be very hard to diagnose.